Differential assemblies are known in the automotive industry as devices that split engine torque two ways, allowing each output to spin at a different speed. Generally, differential assemblies have three primary tasks: to aim the engine power at the wheels; to act as the final gear reduction in the vehicle, slowing the rotational speed of the transmission one final time before transmission to the wheels; and to transmit the power to the wheels while allowing them to rotate at different speeds.
A typical mechanical differential contains a housing (or carrier), two side gears, and several pinion gears. A rotating driveshaft of the vehicle engages a ring gear, which is mounted onto the differential housing. The driveshaft drives the ring gear, which in turn rotates the differential housing. Pinion shafts attach the pinion gears to the housing so that, as the housing rotates, the pinion gears are driven. The pinion gears drive the two side gears, which in turn drive the axle (or half shafts) attached thereto.
The pinion shafts of the differential assembly typically have a support ring that secures to the inward ends of pinion shafts so that the torque of the housing can be transmitted to the pinion shafts and thereby drive the pinion gears. The pinion gears spin upon the pinion shafts and rotate about the axis of the housing.
The conventional support ring is typically a ring-type component having a hollow center with a plurality of apertures provided through the wall of the support ring for receiving the ends of the pinion shafts. This type of support ring is usually made from a hollow tube or pipe. In some cases, the required size of the support ring does not correspond to the size of the standardized tube material supplied in the market. In such cases, manufacturers have been forced to use solid bars that correspond to the required size of the support ring. However, solid bars generally have to be substantially machined to create rings. As such, a large amount of material has to be machined to form a hollow support ring having the required dimensional characteristics.
With reference to FIGS. 1A and 1B, typical mechanical differentials contain a housing 1, two side gears 3, and several pinion gears 4. The pinion gears 4 are fixed to the housing 1 by a pinion shaft 5 so that the pinion gears 4 may be driven by the housing 1 to rotate around the housing 1 while spinning on the pinion shafts 5. Typically, the pinion shafts 5 are rigidly secured to the housing 1 at their respective distal ends, and supported by a support ring 6 at their respective proximal ends. Torque is transmitted to the housing 1, and the housing 1 drives the pinion shafts 5 which in turn drives the pinion gears 4. As the pinion gears 4 move, the pinion gears 4 drive the side gears 3 so that torque may be transmitted to the side gears 3.
FIGS. 2A-2E illustrates a conventional support ring 6 having an outer surface 11 and inner surface 13, with the inner surface 13 defining a hollow center. Typically, three apertures 10 are machined through the outer surface 11 and the inner surface 13 of the support ring 6 to provide connections for the pinion shafts.
During operation of the differential assembly, friction and heat are generated as components within the differential housing are engaging and contacting one another. This friction and heat reduces the durability and load carrying capacity of the differential assembly, such as by causing scoring damage to the contact surfaces. Consequently, in most applications, the differential assembly must guide lubricant to the various frictional surfaces to relieve friction and minimize the generation of heat.
For example, the contact surfaces of the pinion gear bore and pinion shaft 5 are among the important surfaces that require significant lubrication. In many applications, the lubricant for lubricating these surfaces is supplied to the differential through shaft bores 17 and corresponding splined bores 18 of the side gears 3. Under the effect of centrifugal force generated when the differential is rotating, the lubricant flows inwardly thru the shaft bores 17 and splined bores 18, and the lubricant is collected by the inner surface 13 of support ring 6. The lubricant then flows through the clearance between the bores 10 of the support ring 6 and flat features 19 of each pinion shaft 5 to a corresponding interface of the contact pair of the pinion gear bore and pinion shaft 5.
Consequently there exists a significant need for a pinion shaft support structure that is capable of providing lubrication pathways to the interface of the pinion gear bores and pinion shafts, while also capable of reducing the time and expense in machining the support structure thereby resulting in reduced manufacturing costs.